Abstract

The climate change-induced expansion of mangroves into salt marshes could significantly alter the carbon (C) storage capacity of coastal wetlands, which have the highest average C storage per land area among unmanaged terrestrial ecosystems. Mangrove range expansion is occurring globally, but little is known about how these rapid climate-driven shifts may alter ecosystem C storage. Here, we quantify current C stocks in ecotonal wetlands across gradients of marsh- to mangrove-dominance, and use unique chronological maps of vegetation cover to estimate C stock changes from 2003 to 2010 in a 567-km2 wildlife refuge in the mangrove-salt marsh ecotone. We report that over the 7-yr. period, total wetland C stocks increased 22 % due to mangrove encroachment into salt marshes. Newly established mangrove stands stored twice as much C on a per area basis as salt marsh primarily due to differences in aboveground biomass, and mangrove cover increased by 69 % during this short time interval. Wetland C storage within the wildlife refuge increased at a rate of 2.7 Mg C ha−1 yr.−1, more than doubling the naturally high coastal wetland C sequestration rates. Mangrove expansion could account for a globally significant increase of terrestrial C storage, which may exert a considerable negative feedback on warming.

Notes

Acknowledgments

Funding for this work was provided by grants from the National Aeronautics and Space Administration Climate and Biological Response Program (NNX11AO94G, NNX12AF55G) and the National Science Foundation Macrosystems Biology Program (EF 1065821). This work was conducted as part of NASA’s Climate Adaptation Science Investigators (CASI) Workgroup. Cheryl Doughty was also supported by a Link Graduate Fellowship at the Smithsonian Marine Station in Fort Pierce, FL (SMSFP Contribution No. 986). We would like to thank Glenn Coldren, Loraé Simpson, Joseph Funk and Regina Kukola for support in field collections, Courtney Curran and Julie Kurtz for sample preparation, and Lisa Duckett for C:N sample analysis. We also acknowledge Jim Lyon from the U.S. Fish and Wildlife Service, and Lynne Phillips and Carlton Hall for continued support from the NASA Kennedy Space Center Environmental and Ecological Programs. Lastly, we thank the editor and the two anonymous reviewers whose suggestions have greatly improved the quality of the manuscript.

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